sharing the space

Sharing the space:  something we often see in nature, where species or individuals divide up the resources in a way that maximizes their gain while reducing competition from closely related individuals.  Some sparrow species seem to be flexible in where they forage, adjusting their resource use based on the presence of other birds.  For example, at the Alviso marina park in the southern San Francisco bay, we saw Song Sparrows, Field Sparrows, and White-crowned Sparrows in the same area of the park, but in quite different micro-habitats.

song sparrow in swamp grass-

This particular Song Sparrow was practicing his song, but only half-heartedly. Just a warm-up before the breeding season gets going.

Song Sparrows were found in brushy areas and dried grasses of the wetland in the park, although they can often be found on the edge of more open, grassy areas in other habitats.

white-crowned sparrow-

Juvenile and adult White-crowned Sparrows foraged in small flocks together. First-year birds have brown and white crowns; adults are a more striking black and white.

White-crowned Sparrows are migrants, overwintering in the lower 48 states but flying as far north as northern Canada and Alaska to breed in the spring.  Some birds may be permanent residents along the California coast, but these particular individuals were not acting territorial.  In the park, the White-crowned sparrows foraged at the base of shrubs and along rocks and logs on the shoreline, picking at the seeds in the litter that accumulates in crevices.  In their higher latitude or altitude breeding sites, they prefer open grassy meadows dotted with small shrubs in which they place their nests.

adult white-crowned sparrow on anise seed-

An adult White-crowned Sparrow perched on a dried wild anise plant gets a better view of where to forage next.

The third species we saw in the park, Field Sparrows, were found in the field (as their name implies), i.e., in grassy meadows dotted with occasional tall annual plants and shrubs.  These birds are typical of “old fields”, areas that are undergoing successional change from cultivation back to shrub and forest.

field sparrow-

Field Sparrows aren’t particularly colorful (except for their pale pink beak), but they sing a song that sounds like a bouncing ball, and are usually easy to spot once you’ve heard them.

These are just a few of the ground-feeding seed-eaters that most likely can be found in the park area:  Golden-crowned Sparrows and Towhees are also seen on occasion.  The variation in habitat throughout the park makes it attractive to a wide diversity of wildlife that can share the rich resources.

3 thoughts on “sharing the space

  1. Pingback: sharing the space — Back Yard Biology | By the Mighty Mumford

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